HTupolev

"Gravel tire" can be an extremely wide net, especially if we define it by what the users are doing. Someone whose gravel roads are constantly turning into clumpy thick mud bogs is potentially going to view aggressive knobbies as "gravel tires." Some gravel tires don't lose anything to performance-oriented road slicks, because they are performance-oriented road slicks. I know people who run beefy commuter road slicks for gravel... these are sometimes just as slow on pavement as tires marketed as "gravel tires."

I wouldn't go by feel, it's very hard to guess with any kind of precision. But differences of a couple mph wouldn't be hugely shocking between a fast road tire and a slow gravel tire.
When I first built up my gravel bike, I got a pair of Double Fighter IIs for $10 and threw them on. On pavement, I tended to end up around 10% slower compared with similar efforts on my road bikes. The bike still can't climb paved mountains as well as my road bikes due to its extreme weight, but when I have Rat Trap Pass ELs installed, in can trade blows with them on the flats.

If you need the tread and want to minimize the performance hit, consider minimizing the protection. I'd guess the folding version of the Continental Cyclocross Speed is decently fast, based on its specs. For something with some knobs for serious mud riding, maybe the Compass Steilacoom.